The distribution of core histones to daughter DNA molecules has been studied. No evidence was found for preferential association of core histones with the DNA synthesized in the same cell generation. Preliminary experiments have developed a method for examining the distribution of proteins which remain associated with the DNA in 2MNaC1. The distribution of these poteins during cell replication is now being analyzed. Conditions for differential digestion of substituted and unsubstituted chromatin are being explored. SV40 minichromosomes will be used as a model system to optimize digestion conditions. Separation of HL and LL chromatin by by brief irradiation wit ultraviolet light followed by digestion with S1 nuclease appears promising. These methods will be used for the study of segregation of nonhistone proteins. The existence of a programmed appearance of histone subtypes during embryogensis of the sea urchin Lytechinus variegatus is being probed.